A study of the current distribution, electro-magnetic response function, and proximity effect in superconducting amorphous Bi films

Abstract

Kinetic inductance measurements have been used to probe the degree of current distribution uniformity that exists within thin superconducting amorphous Bi films. These measurements were made on films having various cross-sections which were condensed on both quartz plates and Nb shield planes. The Nb shield plane appeared to smooth the current distribution considerably. Measurements of the kinetic inductance were also used to determine the temperature dependence of the electromagnetic response function in amorphous Bi films. The zero temperature response function for these films was evaluated using strong-coupling theory and gap parameter data derived from tunneling measurements. With this value for the response function, an unambiguous determination of the zero temperature penetration depth, λ (0), was possible. The proximity effect, which occurs when a normal metal is placed in good electrical contact with a superconductor, was studied using measurements of the kinetic inductance of amorphous Bi films both before and after deposition of a normal overlayer. Data on the transition temperatures of films with and without a normal overlayer were fitted to the Werthamer theory of the proximity effect. From this fit, the value of the electromagnetic coherence length in amorphous Bi was determined. The added temperature dependent effect produced by an Fe overlayer on the kinetic inductance of a Bi film has been shown to be well explained by the theory of Fulde and Moormann for the spacial dependence of the order parameter.